This study aims to analyze macrophage differentiation antigens and heterogeneity. We will use monoclonal antibodies against monocyte differentiation antigens to analyze the expression of these antigens on bone marrow progenitor cells and on various tissue macrophages. In particular, we will make an attempt to analyze the antigenic makeup of macrophages obtained from normal and pathological lymph nodes as well as alveolar macrophages using immunofluorescence and immunoperoxidase techniques. In addition, we will analyze the effect of soluble mediators such as interferon and lymphokines on the expression of various monocyte differentiation antigens. Finally, monoclonal antibodies will be used as a probe to determine the origin of the abnormal cells in "histiocytic" disorders and lymphomas such as Hodgkin's disease. (HI)